The present invention relates to apparatus for finishing the cylindrical interior of long cylindrical tubes, such as those used in hydraulic cylinders.
A hydraulic or pneumatic cylinder is typically roughly formed in a steel mill by drawing a steel blank over a mandrel. As the steel is drawn over the mandrel, particulate matter often becomes embedded in the interior surfaces of the cylinder, and imperfections in the mandrel form corresponding imperfections in the interior of the cylinder. As a result, the interior surfaces of the cylinder must be finished so that the cylinder is usable for hydraulic and pneumatic applications.
Combined skiving and roller burnishing tools, such as that shown in U.S. Pat. No. 4,367,576, are currently available which both cut (skive) the interior of a cylinder to its approximate final diameter, and roller burnish the interior of the cylinder so that it has a smooth finish. Such combined tools conventionally include a skiving tool followed by a plurality of circumferentially spaced rollers in a roller cage. The skiving tool has oppositely disposed knife blades which each produce a helically shaped chip of cut material. The rollers are biased against the cut surface to remove imperfections caused by the skiving process.
Combined skiving and roller burnishing tools have the advantage of cutting and finishing the interior of the cylinder in a single operation, but their use has been found to have certain drawbacks. The skiving and roller burnishing tools described above typically have nylon pads behind the skiving knives and proximate the rollers to stabilize the roller burnishing action of the tool. When attempts have been made to locate such pads in front of the skiving knives, they tend to wear with use, and when worn, often cause chattering of the tool, which ruins the cylinder finish. In addition, the skiving operation creates a helical chip which is directed forwardly out the far end of the tube past the forward portion of the skiving and roller burnishing tool. Coolant flow helps direct the chip out the forward end of the tool. Potential contact between the chip and forwardly located pads has been a significant problem which can destroy a cylinder and sometimes the expensive tool. The use of such nylon pads has thus generally been confined to locations aft of the skiving knife.
While the combined skiving and roller burnishing tools of the type described above are generally functional and provide high quality finished cylinders, their use on very long cylindrical bores can be problematic. It will be appreciated that when cutting and finishing a cylinder, it is desirable that only the cutting tool and the burnishing rollers be in contact with the interior cylindrical wall. Contact between any other portions of the tool and the cylindrical wall can scratch or mar the surface which, of course, is undesirable. Such limited contact between the tool and the cylindrical wall can lead to misalignment of the tool, particularly when very long bores are being finished.
The tools are mounted on drive members and the long drive members required for very long bores will not be completely rigid. Any bending in the drive member can cause the knife blade to oscillate or wobble, causing minor undulations in the finished cylindrical wall. While such undulations may be very small, they may often exceed the close tolerances required for critical applications. It would thus be desirable to provide a skiving and roller burnishing tool which will remain axially aligned with the cylinder despite bending in the associated drive member and is capable of finishing relatively long cylindrical bores within very close tolerances.
The present invention provides apparatus for finishing the inside of hollow work-pieces such as long hydraulic or pneumatic cylinders. A rotatable skiving and roller burnishing tool is advanced into one end of the work-piece and advanced through the cylindrical interior of the work-piece. The skiving section is located at the front of the skiving and roller burnishing tool, and the roller burnishing section comprises the rearward section of the tool. The skiving section of the tool has a knife holding portion which holds a skiving knife to skive the interior from a start diameter to a larger, finish diameter. The skiving section also has a plurality of cavities, forward of the knife holding section, which are disposed circumferentially around the skiving section of the tool. A plurality of probe centering location finders are located in the respective cavities. The radial positions of the probe centering location finders are independently adjusted to properly center the skiving and roller burnishing tool as it is advanced through the cylinder.
The probe centering location finders located in the tool of the skiving and roller burnishing tool are preferably made of aluminum bronze alloy. This alloy is very hard relative to other potential materials, and has been found to hold up relatively well when subjected to the wear caused by the motion of the skiving and roller burnishing tool. The alloy is able to slide against the inside of the tube with a desirable amount of friction, while maintaining its physical integrity despite the heat generated by the rotation of the skiving and roller burnishing tool. The use of this hard alloy allows the placement of the finders in advance of the knife location without excess deterioration, as was the case with nylon spacers attempted in the past. The finders secure the skiving and roller burnishing tool as it progresses further away from the point at which the tool entered the cylinder, allowing the finishing of cylinders over 20 feet long to within tolerances of a few thousandth""s of an inch.
The configuration of the probe centering location finders of the preferred embodiment have also been found to be advantageous. Each probe centering location finder of the preferred embodiment has a generally cylindrical outer surface, a sector of which is planar. Each finder in that embodiment has radially disposed threaded aperture, and the tool has lateral threaded apertures intersecting each cavity. Adjustment screws are employed in the radial apertures to set the radial location of each finder relative to the base of the cavity, and securing screws are employed in the lateral apertures to fix the adjusted position of the finders. The planar sector on each finder provides a flat surface on which the securing screw can contact the probe centering location finder and thus hold it in place.
The preferred embodiment of the present invention further provides for a straighter boring of a cylinder by allowing the knife holder to float freely in a radial direction. The knife holder is located within a polygonal aperture in the knife holding section, which extends through the skiving section of the tool. The knife holding section has a corresponding polygonal shape and is allowed to roll on a plurality of roller bearings which are disposed on the inner surfaces of the knife holding section. Allowing the knife holder to move freely, as opposed to securing it in a fixed position to the skiving and roller burnishing tool, allows the knife holder to be self-centering while the tool rotates. Additionally, this floatation reduces the amount of friction between the knife blade and the inside wall of the tube which allows the knife to follow the bore of the tube more closely.
In conventional skiving and roller burnishing tools, the helical chips created by the knife blades can impede the procession of the skiving and roller burnishing tool if they are not properly removed from the area in which the skiving and roller burnishing tool is operating. In order to remove the chip as efficiently as possible, a coolant is pumped through the tube from the end at which the skiving and roller burnishing tool entered. The coolant is channeled through a pair of longitudinal indentations on opposite sides of the skiving portion of the tool so that the coolant passes over the knife locations. The knife blade is continuously cooled and the chip is continuously pushed forward and away from the knife holding section of the tool.
The preferred embodiment of the present invention provides two frustoconical sections, opening forwardly, at the forward end of the indentations. These sections direct the coolant flow, and act to shape the chips and direct their removal away from the tool. The locations of the multiple probe centering location finders is significant in this process because, if positioned incorrectly, they re-present places at which the chip could get entangled while passing through the front of the tool. By placing a pair of probe centering location finders between the frustoconical sections on either side in the preferred embodiment, and positioning the two probe centering location finders in each pair roughly sixty degrees apart, the chances of the chip being hindered while passing the front portion of the tool are minimized.
The novel features which are characteristic of the invention, as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which a preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.